Our overall objective is to understand why the immune system in SLE (lupus) responds abnormally to nuclear autoantigens from cells undergoing physiologically programmed apoptosis, and how this response could be specifically downregulated for effective therapy? We have found that autoimmune T and B cells of lupus recognize certain critical histone peptide epitope/s from nucleosomes, which in a low-dose tolerance regimen blocks pathogenesis and progression of lupus by inducing potent regulatory T-cell (Treg) subsets. The induced Treg cells suppress autoimmune T helper (Th) cells, B cells and autoantigen presenting cells (APC), as well as inflammatory cell infiltration in kidneys and blood vessels in lupus. This therapy in SNF1 mice with spontaneous SLE, generates tolerogenic plasmacytoid dendritic cells (pDC) that cause expansion of autoantigen-specific Treg cells and contraction of autoimmune and inflammatory Th1 and Th17 cells. We propose to define molecular changes at the cell-surface and inside the cell that cause an increased TGF21 and decreased IL-6 expression program in the tolerogenic pDC. We will also devise a culture system for inducing low-dose peptide tolerance in vitro using lupus mouse cells to be used for defining toll-like receptor (TLR) and other signals in tolerance mechanisms, and for future application to screen tolerogenic peptides in lupus patients. Secondly, although nuclear antigens derived from apoptotic cells participate in cognate interactions between autoimmune Th cells and B cells in lupus leading to production of pathogenic anti-DNA autoantibodies, the initial steps are not known. In order to give help to autoimmune B cells, autoimmune CD4+ Th cells are required to be initially activated (primed) by APCs which present autoantigen particles, such as nucleosomes and ribonuclear protein complex from apoptotic cells. We have found that CD117+ cells in splenocytes of lupus-prone SNF1 mice present apoptotic nuclear autoantigen particles much more efficiently than conventional APCs (B cells, DC and Macrophages) to activate autoimmune Th1 and Th17 cells simultaneously. CD117 (c-Kit), a receptor for stem cell factor, is a marker expressed by macrophage/DC progenitor (MDP) cells, common DC precursor (CDP) cells, and mast cells. Therefore, we need to identify which lineage of cells the novel CD117+ APCs belong. We will also study the role of the novel APC in breaking B and T cell tolerance in lupus and other autoimmune diseases, identify other unique markers they may have, and study the molecular requirements for their unusual ability to present nuclear autoantigens to activate both Th1 and Th17 cells in lupus. Thus, our hypotheses and ensuing aims are focused on antigen presenting cells (APCs), to determine how novel APCs initiate breakdown of tolerance to nuclear antigens from apoptotic cells to induce pathogenic Th1 and Th17 responses simultaneously in lupus and how this priming step can be blocked;and conversely how other APCs, such as pDC can restore immunoregulation after antigen specific tolerance therapy of lupus. PUBLIC HEALTH RELEVANCE: We have invented and developed a non-toxic, antigen-specific tolerance therapy targeted against autoimmune cells that would spare SLE or lupus patients from receiving mutagenic cytotoxic agents, corticosteroids and global immunosuppressants. The therapy is also aimed at maintaining lupus patients in remission, and preventing the initiation or progression of organ damaging disease in patients at risk. In this application we will define how the therapy works to restore normal regulation of the immune system in lupus, and how it can be improved further. A detailed understanding of the mechanisms would rapidly bring this therapy to patients in the clinic. The proposed studies will also provide a better definition disease pathogenesis initiated by a novel antigen-presenting cell inducing autoimmune response in not only lupus, but also other autoimmune inflammatory diseases, such as rheumatoid arthritis, multiple sclerosis, and insulin-dependent diabetes mellitus. Collectively, these diseases affect tens of millions of Americans, resulting in considerable morbidity (sickness), mortality (death), pain and suffering, and medical costs. The studies would help in devising specific means to block the initial steps of tolerance breakdown in major autoimmune diseases.